• Support PF! Buy your school textbooks, materials and every day products Here!

Molecular physics (easy stupid questions )

  • Thread starter goneftw
  • Start date
  • #1
3
0
[PLAIN]http://img560.imageshack.us/img560/6712/fizika5.jpg [Broken]

Homework Statement


The electric energy is used to heat the liquid in the metalic bowl..

1.Why is the liquid warmer at the top of the bowl than the bottom?
2. Why does the liquid's temperature raise faster if the metalic bowl has a cover on?
3. In this experiment, is it possible that liquid's temperature doesn't raise up even then if the current is flowing through the coil? And why it is/isn't possible ?

4. Bowl has 0.5 kg of water in it. the heater gives heat to the water at rate of 36 J/s.
4.1*Calculate the speed of temperature's raising(Kelvin/min), if the water's specific heat is 4200 J/(Kg*K). You can ignore the bowl's specific heat....
4.2* If you don't ignore the bowl's specific heat then how does it affect the calculated temperetue's raising speed ? Why ?



Homework Equations


Q=c*m(t1-t2) Q-heat quantity, c-specific heat, m-mass of water,t-temperature


The Attempt at a Solution



1. Because when the coil heats the water molicules the molicules start moving faster and the pressure gets higher and the molecules rises up ?
2.Because the heat which would flow away without the cover now would make a a bigger pressure in the bowl and the process would happen much faster...
3.I really don't know, please someone explain this to me :(
4. I think i'm absolutely wrong with this one : Q=c*m(t1-t2) t1-t2=36*2/4200=0.017
4.2 don't know
 
Last edited by a moderator:

Answers and Replies

  • #2
58
0
1) Why would they move up ? Why not down because of gravity ? Think of what heat does to density of a liquid or gaz.

2)Liquid gets warm and expands----> pressure(bowl sealed)----> molecules want to "relax" and be at a more stable energy level, but they can't since the bowl has been sealed--->and with current still present there is no cooling, only heating. When Bowl was open there was some sort of cooling, a convection was happening.

3) What do you think will happen if the water starts boiling ? The molecules of liquid can always be heated up and start moving in all sorts of directions.

4) you can express Q=m*c(deltaT) as a function of heat with respect to time and differentiate it with respect to time. mass and specific heat would be the constants.
 

Related Threads for: Molecular physics (easy stupid questions )

  • Last Post
Replies
15
Views
5K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
13
Views
846
  • Last Post
Replies
2
Views
900
  • Last Post
Replies
13
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
12K
  • Last Post
Replies
6
Views
2K
Top